stuck in emergency mode,can't use LG support tool

I flashed this rom:
csmg.lgmobile.com:9002/swdata/WEBSW/LGKH5200/AKTFBQ/V10r_00/V10R_00.kdz

I changed some files of my system,installed busybox,now I can't boot.I tried to enter fastboot,but failed,maybe LG closed the fastboot keys.But I still can enter emergency mode,how can I reflash my phone with system.img again?